Investigations into the interrelationships between energy metabolism (oxidative phosphorylation), characteristics and specificity of biological membranes and intracellular metabolic regulation will be studied at several levels of tissue organization. Isolated perfused hearts and perfused rat hind quarters will be employed to evaluate both qualitative and quantitative aspects of anaplerotic reactions to the citric acid cycle in heart and skeletal muscle. The effects of diet and physiological state on these pathways will be evaluated. The NAD- and NADP-specific 'malic' enzymes which we have observed to be present in heart mitochondria will be further characterized. The transfer of reducing power across the mitochondrial membrane is mediated by substrate shuttle systems which are regulated by exchange enzymes in the membrane and, in turn, by the 'energy pressure' of the system. Cell- free in vitro systems containing liver mitochondria and cytoplasmic enzymes and a 'physiological' energy load and, later, isolated whole hepatocytes will be used to evaluate the coupling between energy metabolism, substrate anion transport, intracellular transfer of reducing power and the control of major pathways such as gluconeogenesis and lipogenesis. The relation of morphological state and topographical parameters of enzymes confined within the mitochondrial membranes to metabolic control will be evaluated employing electron microscopy and metabolic functional characteristics.